To examine a body cavity with an endoscope, the flexible pipe of the endoscope is inserted into the body cavity. Since the normal body temperature is about 36.degree. C., the temperature of the body cavity is usually higher than the temperature of the outside air. The humidity in a body cavity is usually very high, about 100%. On the other hand, the temperature of the flexible pipe of the endoscope before it is inserted into the body cavity is substantially that of the ambient air. Accordingly, when the flexible pipe is inserted into the body cavity, its temperature increases. Because of the initial temperature difference, an observing objective lens window provided at the end of the flexible pipe collects moisture.
During observation of the body cavity with the endoscope, sometimes it is necessary to supply air into the body cavity to expand a part of the body cavity or to supply water to the observing objective lens window to remove foreign matter therefrom. In such a case, as the end portion of the flexible pipe of the endoscope is cooled by the air or water, the window collects moisture.
When the objective lens window collects moisture as described above, it is difficult to observe the body cavity which may therefore result in an erroneous diagnosis. Accordingly, it is necessary to carry out diagnostic observation exceedingly carefully so that it takes a relatively long time for adequate observation. Undoubtedly, this inflicts pain on the patient and the operator will tire. Thus, it is necessary to prevent the objective lens window from collecting moisture. Otherwise, undesirable conditions as described above may result. Especially, in photographing the body cavity, moisture collection on the objective lens window must be prevented.
In order to prevent the objective lens window from collecting moisture, heretofore a technique was employed in which, before the endoscope is used, the objective lens window was coated with a hydrophilic lens cleaner such as a liquidstate hydrophilic cleaner or a solid soap. However, the conventional technique is still disadvantageous in the following points. The window surface is covered with the hydrophilic lens cleaner at all times. However, such a solid lens cleaner becomes liquified due to the relatively high temperature of the body cavity and a film layer forms on the objective lens. When observation is made through the film layer, which tends to be wavy, the image observed through the objective lens is distored. That is, the optical performance of the objective lens is significantly lowered with the result that it is rather difficult to make an accurate diagnostic observation of an affected part.
Moreover, the service life of the lens cleaner is reduced and the effect of the lens cleaner is lowered by supplying air or water into the body cavity. As a result, the objective lens window again will collect moisture. Thus, the above-described conventional technique is not entirely suitable for an examination of a body cavity which requires a relatively long time.
Water repellent cleaner has also been employed to coat the objective lens window. The use of a water repellent cleaner is also disadvantageous similar to the case of a hydrophilic lens cleaner. Yet further, a technique utilizing a dry system lens cleaner has also been known in the art. However, that technique involves a problem in that the objective lens window still collects moisture due to the above-described temperature difference.
Accordingly, an object of the present invention is to provide a device for preventing the observing objective lens window from collecting moisture in which the above-described drawbacks accompanying conventional techniques utilizing lens cleaners have been eliminated.